1. Field of the Invention
The present invention relates to a mask and its manufacturing method, and more particularly, to a hybrid phase-shift mask and its manufacturing method.
2. Description of the Previous Technology
Because minimum linewidths have been shrinking, the resolution of the mask (photomask) must be enhanced. As a result, increasingly complex resolution enhancement techniques (RET), for example, off-axis illumination, phase-shift mask, and optical proximity correction, have been required to maintained adequate pattern fidelity. Of the RET, the phase-shift mask (PSM) is expected as a viable alternative. Many forms of PSM, such as alternate PSM, chrome-less PSM, and attenuated PSM, have been developed over the years. They are respectively suitable for specific pattern, and their ability to improve the resolution can be distinguished into strong PSM and weak PSM.
The mask is responsible for transferring the pattern to an underlying substrate. The smaller critical dimension of the substrate will cause the higher need in resolution. Because the substrate may have some region characterized by smaller critical dimension and some region characterized by larger critical dimension, one mask may need high and low-resolution part manufactured at same mask, for printing critical and non-critical features at the same time. For instance, a substrate, employed for liquid crystal display, a lot of alternate lines and spaces characterize its central region, and a lot of irregular lines or shapes, used for logical control, characterize its periphery region. Comparing the resolution-enhanced ability of the phase-shift masks, the alternate PSM and the chrome-less PSM are comparable, the alternate PSM and chrome-less PSM are stronger than the attenuated PSM, and the attenuated PSM is stronger than the Binary mask. The alternate PSM or chrome-less is suitable for patterning the shape of line and space, but not suitable for irregular shapes within the periphery region. In the context of manufacturing alternate PSM or chrome-less PSM masks, mask fabrication should meet process issues such as phase uniformity control and defect repair control, both of which can be challenging. The attenuated PSM can be used for both the line/space and irregular shapes of logical pattern. Nevertheless, if the line is critical, as in 0.14 μm, it will fail to reach the demand of resolution.
To improve the resolution, the advanced photolithography process can use two or more masks, such as one chrome-less PSM and one attenuated PSM, to expose the substrate two, even multiple times. Although this process enhanced the resolution, it also wastes time and higher process defect risk. A hybrid mask could be another solution. It has two different mask topography structures for patterning. Manufacturing a hybrid mask often needs more complex materials and consequently more films, therefore resulting in more steps and difficulty in the manufacturing process.
Accordingly, we need a hybrid phase-shift mask that allows for printing critical and non-critical features at one exposure process, and the manufacturing process of the hybrid mask can be simplified, for saving time and increasing yield.